Synchronizer rings have been conventionally used, for example, in synchromesh gear transmissions. Such synchronizer ring is a friction ring that engages in synchronized sliding with its rotating counterpart member, for example, a tapered cone, and disengages with the tapered cone. The ring plays an important role in synchronization of peripheral speeds of two mutually engaged gears. A synchronizer ring is known to have a structure, as shown in FIG. 1, where multiple gear teeth 100, adapted to engage with a counterpart member (not shown), are disposed, with a predetermined spacing, on the external-most circumference of a synchronizer ring, an internal circumferential surface 101, adapted to make contact with a tapered cone (not shown) when engaged, has longitudinal grooves 103 disposed thereon, and, when required, ring-shaped thin stripe grooves 102 formed thereon at a right angle with longitudinal grooves 103, and an external circumferential surface has keyways 104 disposed thereon for a synchrozizer key (not shown) to fit. Brass (a Cu--Zn alloy) has been typically used as material for forming a synchronizer ring.
With a synchronizer ring having chances to be formed in such shape, for example, as one described above, it is typically required that the ring has high mechanical strength and precision, and, besides, its internal circumferential surface, adapted to make contact with its counterpart member when engaged, has both excellent frictional characteristics and ample scuffing resistance. Especially, in the field of automotive transmissions, since not only secured functionality but also luxurious and sportive feeling are looked for in the operation as transmissions recently tend to be more luxurious and have higher performance, a synchronizer ring is desired that has further improved frictional characteristics and scuffing resistance.
Thus, various types of synchronizer rings are being studied that are attempted to have frictional characteristics and scuffing resistance improved, compared to conventional synchronizer rings made of brass (a Cu--Zn alloy).
Specifically, a synchronizer ring is known where a layer is formed on its internal circumferential surface by means of a flame-spraying method, the layer being prepared by uniformly mixing metal with ceramics and oxide, and fusing them together, as disclosed in JP-B 46-15043. Also, as a method available for manufacturing synchronizer rings, for example, a method for manufacturing a friction ring is known where a friction lining is formed on its internal circumferential surface by means of a flame-injecting method, the lining comprising sintered powder containing an 80 weight percent of metallic component powder and a 20 weight percent of non-metallic component powder, as disclosed in DE-PS 3,705,661.
Furthermore, a synchronizer ring is also being studied that comprises Fe-based sintered alloy containing bainite, pearlite and free Cu-phase in its base body.
However, the required frictional characteristics and scuffing resistance have not been accomplished yet with such conventional synchronizer rings as disclosed above, including the synchronizer rings having a layer formed on its internal circumferential surface by means of a flame-spraying method, the layer being prepared by uniformly mixing metal with ceramics and oxide, and fusing them together, and the synchronizer rings obtained by employing the method for manufacturing a friction ring where a friction lining is formed on its internal circumferential surface by means of a flame-injecting method, the lining comprising sintered powder containing an 80 weight percent of metallic component powder and a 20 weight percent of non-metallic component powder.
Other problems also having been experienced are such as insufficient strength due to insufficient dispersion of each metallic component, and unstable quality due to irregularity in the material of flame-sprayed coating. Furthermore, particles incompletely fused in the flame, or splashed or rebounded particles, are often entrained in the surface layer of flame-sprayed coating. Such entrained particles cause such problems that frictional characteristics tend to vary as time elapses due to the surface made rough by the entrained particles, and various portions in the transmission are caused to wear due to the entrained particles dropping off. On the other hand, grinding and cutting were being applied to the surface of the flame-sprayed coating for reducing the surface roughness of the coating. Disadvantageously, however, such grinding or cutting caused high working cost and material loss due to working margin.
In addition, the synchronizer ring comprising Fe-based 6 sintered alloy containing bainite, pearlite and free Cu-phase in its base body, as discussed above, has disadvantage in that sizing is difficult to work due to high hardness of HRB 90 caused by the contained bainite. Besides, coefficient of dynamic friction still has room for improvement.
The present invention has been made to solve the problems and overcome disadvantages, described above. Thus, an object of the present invention is to provide a synchronizer ring having excellent frictional characteristics and scuffing resistance and stable quality.